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The herbicide glyphosate has been widely used in the past 40 years, under the assumption that side effects were minimal. In recent years, its impact on microbial compositions and potential indirect effects on plant, animal and human health have been strongly suspected. Glyphosate and co-formulates have been detected in various water sources, but our understanding of their potential effects on aquatic animals is still in its infancy compared with mammals. In this study, we investigated the effect of chronic exposure to an environmentally relevant concentration of glyphosate on bacterial communities of rainbow trout (Oncorhynchus mykiss). Gills, gut contents and gut epithelia were then analyzed by metabarcoding targeting the 16S rRNA gene. Our results revealed that rainbow trout has its own bacterial communities that differ from their surrounding habitats and possess microbiomes specific to these three compartments. The glyphosate-based herbicide treatment significantly affected the gill microbiome, with a decrease in diversity. Glyphosate treatments disrupted microbial taxonomic composition and some bacteria seem to be sensitive to this environmental pollutant. Lastly, co-occurrence networks showed that microbial interactions in gills tended to decrease with chemical exposure. These results demonstrate that glyphosate could affect microbiota associated with aquaculture fish.

International audience; In recent years, a growing number of studies sought to examine the composition and the determinants of the gut microflora in marine animals, including fish. For tropical tuna, which are among the most consumed fish worldwide, there is scarce information on their enteric bacterial communities and how they evolve during fish growth. In this study, we used metabarcoding of the 16S rDNA gene to (1) describe the diversity and composition of the gut bacteriome in the three most fished tuna species (skipjack, yellowfin and bigeye), and (2) to examine its intra-specific variability from juveniles to larger adults. Although there was a remarkable convergence of taxonomic richness and bacterial composition between yellowfin and bigeyes tuna, the gut bacteriome of skipjack tuna was distinct from the other two species. Throughout fish growth, the enteric bacteriome of yellowfin and bigeyes also showed significant modifications, while that of skipjack tuna remained relatively homogeneous. Finally, our results suggest that the gut bacteriome of marine fish may not always be subject to structural modifications during their growth, especially in species that maintain a steady feeding behavior during their lifetime.

Thermophilic spore-forming bacteria are potential contaminants in several industrial sectors involving high temperatures (40-65 °C) in the manufacturing process. Among those thermophilic spore-forming bacteria, Thermoanaerobacterium thermosaccharolyticum, called "the swelling canned food spoiler", has generated interest over the last decade in the food sector. The aim of this study was to investigate and to model pH effect on growth, heat resistance and recovery abilities after a heat-treatment of T. thermosaccharolyticum DSM 571. Growth and sporulation were conducted on reinforced clostridium media and liver broth respectively. The highest spore heat resistances and the greatest recovery ability after a heat-treatment were obtained at pH condition allowing maximal growth rate. Growth and sporulation boundaries were estimated, then models using growth limits as main parameters were extended to describe and quantify the effect of pH on recovery of injured spores after a heat-treatment. So, cardinal values were used as a single set of parameters to describe growth, sporulation and recovery abilities. Besides, this work suggests that T. thermosaccharolyticum preserve its ability for germination and outgrowth after a heat-treatment at a low pH where other high resistant spore-forming bacteria like Geobacillus stearothermophilus are unable to grow.

The shrimp Rimicaris exoculata dominates several hydrothermal vent ecosystems of the Mid-Atlantic Ridge and is thought to be a primary consumer harbouring a chemoautotrophic bacterial community in its gill chamber. The aim of the present study was to test current hypotheses concerning the epibiont’s chemoautotrophy, and the mutualistic character of this association. In-vivo experiments were carried out in a pressurised aquarium with isotope-labelled inorganic carbon (NaH13CO3 and NaH14CO3) in the presence of two different electron donors (Na2S2O3 and Fe2+) and with radiolabelled organic compounds (14C-acetate and 3H-lysine) chosen as potential bacterial substrates and/or metabolic by-products in experiments mimicking transfer of small biomolecules from epibionts to host. The bacterial epibionts were found to assimilate inorganic carbon by chemoautotrophy, but many of them (thick filaments of epsilonproteobacteria) appeared versatile and able to switch between electron donors, including organic compounds (heterotrophic acetate and lysine uptake). At least some of them (thin filamentous gammaproteobacteria) also seem capable of internal energy storage that could supply chemosynthetic metabolism for hours under conditions of electron donor deprivation. As direct nutritional transfer from bacteria to host was detected, the association appears as true mutualism. Import of soluble bacterial products occurs by permeation across the gill chamber integument, rather than via the digestive tract. This first demonstration of such capabilities in a decapod crustacean supports the previously discarded hypothesis of transtegumental absorption of dissolved organic matter or carbon as a common nutritional pathway.

Despite multiple advances in cancer therapies, patients with glioblastoma (GBM) still have a poor prognosis. Numerous glioma models are used not only for the development of innovative therapies but also to optimize conventional ones. Given the significance of hypoxia in drug and radiation resistance and that hypoxia is widely observed among GBM, the establishment of a reliable method to map hypoxia in preclinical human models may contribute to the discovery and translation of future and more targeted therapies. The aim of this study was to compare the hypoxic status of two commonly used human orthotopic glioma models (U87 and U251) developed in rats and studied by noninvasive hypoxia imaging with 3-[18F]fluoro-1-(2-nitro-1-imidazolyl)-2-propanol-micro-positron emission tomography ([18F]-FMISO-μPET). In parallel, because of the relationships between angiogenesis and hypoxia, we used magnetic resonance imaging (MRI), histology, and immunohistochemistry to characterize the tumoral vasculature. Although all tumors were detectable in T2-weighted MRI and 2-deoxy-2-[18F]fluoro-d-glucose-μPET, only the U251 model exhibited [18F]-FMISO uptake. Additionally, the U251 tumors were less densely vascularized than U87 tumors. Our study demonstrates the benefits of noninvasive imaging of hypoxia in preclinical models to define the most reliable one for translation of future therapies to clinic based on the importance of intratumoral oxygen tension for the efficacy of chemotherapy and radiotherapy.

The caridean shrimp Rimicaris exoculata dominates the fauna at several Mid-Atlantic Ridge hydrothermal vent sites. This shrimp has an enlarged gill chamber, harboring a dense ectosymbiotic community of chemoautotrophic bacteria associated with mineral oxide deposits. Until now, their acquisition is not fully understood. At three hydrothermal vent sites, we analyzed the epibionts diversity at different moult stages and also in the first stages of the shrimp life (eggs, hatched eggs (with larvae) and juveniles). Hatched eggs associated with young larvae were collected for the first time directly from gravid females at the Logachev vent site during the Serpentine cruise. An approach using 16S rRNA clone libraries, scanning and transmission electron microscopy, and fluorescent in situ hybridization was used. Molecular results and microscope observations indicated a switch in the composition of the bacterial community between early R. exoculata life cycle stage (egg libraries dominated by the Gammaproteobacteria) and later stages (juvenile/adult libraries dominated by the Epsilonproteobacteria). We hypothesized that the epibiotic phylotype composition could vary according to the life stage of the shrimp. Our results confirmed the occurrence of a symbiosis with Gammaproteobacteria and Epsilonproteobacteria, but more complex than previously assumed. We revealed the presence of active type-I methanotrophic bacteria colonizing the cephalothorax of shrimps from the Rainbow site. They were also present on the eggs from the Logachev site. This could be the first 'epibiotic' association between methanotrophic bacteria and hydrothermal vent crustacean. We discuss possible transmission pathways for epibionts linked to the shrimp life cycle. The ISME Journal (2012) 6, 597-609; doi: 10.1038/ismej.2011.133; published online 13 October 2011

Ventiella sulfuris Barnard and Ingram, 1990 is the most abundant amphipod species inhabiting the Eastern Pacific Rise (EPR 9°N) vent fields. This vent-endemic species is frequently encountered near colonies of Pompeii worms Alvinella pompejana. V. sulfuris specimens were collected during the oceanographic cruise LADDER II at the Bio9 (9°50.3' N, 2508 m depth) hydrothermal vent site. Main objectives were to highlight the occurrence of bacterial symbiosis in V. sulfuris and to hypothesise their implications in nutrition. Observations in light and electron microscopy (SEM, TEM) showed that the outer body surface and appendages are free of microorganisms. In contrast, the digestive system revealed two major microbial communities settled in the midgut and in the hindgut. Gut contents showed bacterial traces together with abundant fragments of Alvinellid cuticle and setae, from A. pompejana, suggesting that V. sulfuris could directly feed on Alvinellids and/or on their bacterial epibionts. Molecular analyses based on the 16S rRNA genes revealed the diversity of bacterial communities in the digestive system, of which, the Epsilonproteobacteria phylum, could be considered as one of the major bacterial group. Hypotheses were proposed on their symbiotic features and their implications in V. sulfuris nutrition.

Investigations of the diversity of culturable yeasts at deep-sea hydrothermal sites have suggested possible interactions with endemic fauna. Samples were collected during various oceanographic cruises at the Mid-Atlantic Ridge, South Pacific Basins and East Pacific Rise. Cultures of 32 isolates, mostly associated with animals, were collected. Phylogenetic analyses of 26S rRNA gene sequences revealed that the yeasts belonged to Ascomycota and Basidiomycota phyla, with the identification of several genera: Rhodotorula, Rhodosporidium, Candida, Debaryomyces and Cryptococcus. Those genera are usually isolated from deep-sea environments. To our knowledge, this is the first report of yeasts associated with deep-sea hydrothermal animals.

En libre-accès sur Archimer : http://archimer.ifremer.fr/doc/00000/11142/7919.pdf; International audience; Rimicaris exoculata dominates the megafauna of several Mid-Atlantic Ridge hydrothermal sites. Its gut is full of sulphides and iron-oxide particles and harbours microbial communities. Although a trophic symbiosis has been suggested, their role remains unclear. In vivo starvation experiments in pressurized vessels were performed on shrimps from Rainbow and Trans-Atlantic Geotraverse sites in order to expel the transient gut contents. Microbial communities associated with the gut of starved and reference shrimps were compared using 16S rRNA gene libraries and microscopic observations (light, transmission and scanning electron microscopy and FISH analyses). We show that the gut microbiota of shrimps from both sites included mainly Deferribacteres, Mollicutes, Epsilon- and Gammaproteobacteria. For the first time, we have observed filamentous bacteria, inserted between microvilli of gut epithelial cells. They remained after starvation periods in empty guts, suggesting the occurrence of a resident microbial community. The bacterial community composition was the same regardless of the site, except for Gammaproteobacteria retrieved only in Rainbow specimens. We observed a shift in the composition of the microbiota of long-starved specimens, from the dominance of Deferribacteres to the dominance of Gammaproteobacteria. These results reinforce the hypothesis of a symbiotic relationship between R. exoculata and its gut epibionts.

International audience; Rimicaris exoculata is a deep-sea hydrothermal vent shrimp whose enlarged gill chamber houses a complex trophic epibiotic community. Its gut harbours an autochthonous and distinct microbial community. This species dominates hydrothermal ecosystem megafauna along the Mid-Atlantic Ridge, regardless of contrasting geochemical conditions prevailing in them. Here, the resident gut epibiont community at four contrasted hydrothermal vent sites (Rainbow, TAG, Logatchev and Ashadze) was analysed and compiled with previous data to evaluate the possible influence of site location, using 16S rRNA surveys and microscopic observations (transmission electron microscopy, scanning electron microscopy and fluorescence in situ hybridization analyses). Filamentous epibionts inserted between the epithelial cell microvilli were observed on all examined samples. Results confirmed resident gut community affiliation to Deferribacteres, Mollicutes, Epsilonproteobacteria and to a lesser extent Gammaproteobacteria lineages. Still a single Deferribacteres phylotype was retrieved at all sites. Four Mollicutes-related operational taxonomic units were distinguished, one being only identified on Rainbow specimens. The topology of ribotype median-joining networks illustrated a community diversification possibly following demographic expansions, suggesting a more ancient evolutionary history and/or a larger effective population size at Rainbow. Finally, the gill chamber community distribution was also analysed through ribotype networks based on sequences from R. exoculata collected at the Rainbow, Snake Pit, TAG, Logatchev and Ashadze sites. Results allow the refining of hypotheses on the epibiont role and transmission pathways.

The partial pressure in oxygen remains challenging to map in the brain. Two main strategies exist to obtain surrogate measures of tissue oxygenation: the tissue saturation studied by magnetic resonance imaging (StO2-MRI) and the identification of hypoxia by a positron emission tomography (PET) biomarker with 3-[18F]fluoro-1-(2-nitro-1-imidazolyl)-2-propanol ([18F]-FMISO) as the leading radiopharmaceutical. Nonetheless, a formal validation of StO2-MRI against FMISO-PET has not been performed. The objective of our studies was to compare the two approaches in (a) the normal rat brain when the rats were submitted to hypoxemia; (b) animals implanted with four tumour types differentiated by their oxygenation. Rats were submitted to normoxic and hypoxemic conditions. For the brain tumour experiments, U87-MG, U251-MG, 9L and C6 glioma cells were orthotopically inoculated in rats. For both experiments, StO2-MRI and [18F]-FMISO PET were performed sequentially. Under hypoxemia conditions, StO2-MRI revealed a decrease in oxygen saturation in the brain. Nonetheless, [18F]-FMISO PET, pimonidazole immunohistochemistry and molecular biology were insensitive to hypoxia. Within the context of tumours, StO2-MRI was able to detect hypoxia in the hypoxic models, mimicking [18F]-FMISO PET with high sensitivity/specificity. Altogether, our data clearly support that, in brain pathologies, StO2-MRI could be a robust and specific imaging biomarker to assess hypoxia.